From Scientific American:
Traces of chemicals known to cause human cancer lurk everywhere. But after decades of research, figuring out how many people might contract cancer because of them remains an elusive goal. More than 60 percent of U.S. cancer deaths are caused by smoking and diet. But what about the rest?
A report by the President's Cancer Panel, released earlier this month, reignited a 30-year-old controversy among cancer experts and environmental epidemiologists about how large a role environmental factors play in the No. 2 killer of Americans. Some experts, including the President’s panel, say a decades-old estimate that six percent of cancer deaths are due to environmental and occupational exposures is outdated and far too low. But scientists most likely will never be able to tease out the true role of environmental contaminants because environmental exposures, genetics and lifestyle seem to all intertwine.